1. Field of the Invention
This invention relates to vacuum apparatus for plasma etching semiconductor wafers. More particularly, this invention relates to improved plasma etching apparatus having conductive means for inhibiting arcing caused by charge buildup on insulation members adjacent the wafer.
2. Description of the Related Art
Apparatus for plasma etching semiconductor wafers usually comprises a grounded vacuum chamber in which is centrally positioned a cathode pedestal on the top surface of which the semiconductor wafer to be plasma etched is mounted. The wafer is conventionally secured to the pedestal by a clamping ring mounted on its own support means to permit independent vertical travel. The pedestal, and at least sometimes the clamping ring mechanism, are electrically connected to an rf power supply to permit establishment of a plasma between the cathode pedestal and the grounded chamber during the etch.
Both the pedestal and at least portions of the clamping ring mechanism are constructed of metal, usually aluminum metal, both for purposes of strength as well as to provide electrical connection from the rf power supply to the semiconductor wafer mounted thereon. It is, therefore, necessary to protect such metal surfaces on the cathode, as well as metal and/or plastic surfaces on the clamping ring mechanism, to prevent erosion of such metal or plastic surfaces during the etch. This protection is conventionally provided, at least in part to the metal surfaces, by anodizing the metal surfaces not in immediate contact with the wafer. However, anodization alone does not usually provide sufficient protection due to the porous nature of the oxide film formed by anodizing aluminum.
It is, therefore, customary to also cover the metal surfaces (as well as plastic surfaces, for example, on the clamping ring mechanism) directly facing the grounded chamber with insulation material such as quartz which will not be as easily eroded by the etching environment, and which, in any case, may be easily replaced or renewed without replacing the entire pedestal/clamping ring mechanism.
While such practices do serve to protect the metal parts comprising the pedestal and the metal and plastic parts comprising the clamping ring mechanism, the presence of such insulated surfaces immediately adjacent the plasma path between the grounded chamber and the semiconductor wafer can result in charge buildup on the insulation surfaces which, in turn, can result in arcing, which may cause damage to either the wafer and/or the etching apparatus, i.e., the clamping ring mechanism and/or the pedestal.
In particular, the top surface of the pedestal which serves to support the wafer is usually larger in diameter than the wafer, and the exposed peripheral top surface of the pedestal is usually covered with a quartz ring upon which electrical charges may accumulate. Arcing to the cathode of the charges accumulated on such dielectric surfaces is particularly undesirable because of the potential damage to the wafer, as well as to other adjacent parts of the etching apparatus.
It would, therefore, be desirable to provide improved plasma etching apparatus for the etching of semiconductor wafers wherein arcing resulting from such charge buildup is inhibited while still providing protection for the clamping ring mechanism and pedestal which are exposed to the plasma etch.